Many existing hydroelectric installations are based on Francis turbines, as illustrated in FIG. 1. In these classical installations, the runner wheel 2 turns in the center of a spiral case 4. A stayring 6 with stay vanes 8 at the outlet of the spiral case 4 guides the water to the runner wheel 2. A radial distributor with wicket gates 10 behind the stay vanes 8 controls the water flow and distributes the water evenly around the runner wheel 2. The water passes through the runner wheel 2 and follows its course in a draft tube 12.
Such types of installations are often not very fish friendly due to the reduced dimensions of the water passage through the turbine, the speed of the water flow, the water pressure variations across the turbine, the shear in the water flow, etc. The many parts of the turbine which stand in the way, like the stay vanes, the wicket gates, possible axial or radial distributors, and the runner wheel, form as many hazards for the fish.
Existing methods of increasing the power of hydraulic turbines generally consist of increasing the size of the various parts of the installations, which requires more space. Unless spare space is readily available, the power of the existing installations cannot be increased easily in this way.
U.S. Pat. No. 1,942,995 (BIGGS); U.S. Pat. No. 3,132,839 (HAEKAL); U.S. Pat. No. 3,305,215 (SWIECICKI et al.); U.S. Pat. No. 3,398,696 (SPROULE); U.S. Pat. No. 4,120,602 (MEGNINT); U.S. Pat. No. 4,146,351 (KOELLER); U.S. Pat. No. 4,242,289 (BLUM); U.S. Pat. No. 4,575,307 (SHINOHARA); U.S. Pat. No. 4,780,051 (FISHER, JR.); U.S, Pat. No. 4,867,636 (SAURON et al.); U.S. Pat. No. 5,082,425 (REIL et al.); U.S. Pat. No. 5,261,787 (MORGUNOV); U.S. Pat. No. 5,441,384 (GOKHMAN); U.S. Pat. No. 5,471,965 (KAPICH); U.S. Pat. No. 5,823,740 (CYBULARZ et al.); U.S. Pat. No. 5,879,130 (BEYER et al.); U.S. Pat. No. 5,924,842 (BEYER et al.); U.S. Pat. No. 5,924,844 (CYBULARZ et al.); U.S. Pat. No. 5,941,682 (CYBULARZ et al.); U.S. Pat. No. 5,997,242 (HECKER et al.); U.S. Pat. No. 6,036,434 (RAY et al.); U.S. Pat. No. 6,095,749 (BEYER et al.); U.S. Pat. No. 6,114,773 (KOURIS); U.S. Pat. No. 6,152,684 (FERME et al.); U.S. Pat. No. 6,155,783 (BEYER); U.S. Pat. No. 6,227,798 (DEMERS et al.); and U.S. Pat. No. 6,247,893 (BEYER et al.) provide examples of various other hydraulic turbines and hydroelectric installations of the prior art.